1. Field of the Invention
The present invention relates to a device and a system for grounding shielded cables as they pass through bulkheads or shielded walls.
2. The Prior Art
For electrical shielding and/or safety reasons, it is known to run cables through shield walls and bulkheads, for example on ships, in power plants, computer centers, etc. These systems consist of several bulkhead modules within the bulkheads or shield walls. The area on either side of the bulkhead are separated from each other. The bulkhead provides a seal against water and gas, and also operates as a fire wall.
Electrical signal cables or coaxial cables have one or more shields for protecting the central conductor from electric, magnetic and/or electromagnetic fields. If the cables pass through bulkheads or shield walls, they must be grounded. Accordingly, systems have been designed where the cable shielding is grounded as it passes through the bulkhead or shield wall. With the known systems, the cable is sealed to the two outer sides of the bulkhead. Within the bulkhead, the outer cable insulation and any other inner insulation , if present, are removed over a length of several centimeters, so that the cable shields are exposed. A silver casting mass based on a synthetic resin casting compound having a high concentration of silver particles is poured into the interior of the bulkhead. Following curing of the silver casting mass, a workable contact between the cable shield and a potential-free ground is achieved.
However, these prior art systems have numerous drawbacks including the unfavorable electrical conductivity of silver casting masses as compared to the conductivity of pure metal. The casting mass principle is very costly because of the high percent of silver used, among other reasons. Furthermore, in many applications, particularly ship-building with highly limited space conditions, filling the systems with the silver casting mass presents problems. Another serious drawback is that silver casting masses may become brittle over time. Vibration and changing thermal stresses may cause the silver mass to tear, so that the functional safety of the system is compromised over time. Furthermore, a chemical incompatibility may exist between the synthetic resin casting compound and the shield or insulation of the cable. This may lead to the deterioration of the cable with high consequential damages. This problem is particularly significant if the cable and the silver casting mass of different manufacturers are not chemically compatible with each other.